Finned tubing



A. STEBBINS FINNED TUBING Oct. 28, 1958 Filed Feb. 23, 1956 IN V EN TOR. A RTHUR .srsaams AT TORNEYS I United States Patent Otfice 2,858,115 Patented Oct. 28, 1958 FINNED TUBING Arthur Stebbins, Massapequa, N. Y.; Esther B. Stebbius, administratrix of said Arthur Stebbins, deceased Application February 23, 1956, Serial No. 567,220

6 Claims. (Cl. 257 -262.16)

This invention relates to finned tubing adapted for use in heat exchange apparatus, and pertains particularly to thin wall finned tubing adapted especially for use in air heating systems in which heated gases pass through the tubing in which relatively low pressure differentials exist between the inside and outside of the tube. Such air heating systems are widely used for ovens, dryers, space heating and the like.

It is an object of the invention to provide such tubing which can be fabricated entirely from sheet metal. By utilizing sheet metal, such tubing can be made from relatively thin gauge strip material, which makes possible the fabrication of light weight tubing. Also a wide variety of metals and metal alloys can be used to satisfy various requirements of temperature, corrosion resistance and the like.

. It is a further object of the invention to provide tubing in which the fins extend through the wall of the tubing and are in direct contact with the gases within the tubing, thereby improving the rate of heat transfer.

it is a further object of the invention to provide tubing which can be made in a wide range of diameters including very large diameter tubing suitable for waste heat reclamation.

Other objects and advantages of the invention will appear hereinafter.

A preferred embodiment of the invention selected for purposes of illustration is shown in the accompanying drawings, in which,

Figure l is a perspective view of a section of a strip of sheet metal which has been punched ready for fabrication according to my invention.

Figure 2 is an enlarged section on the line 2-2 of Figure 1.

Figure 3 is a perspective view showing the first step in fabricating the tubing by bending the strip of Figure 1 to semi-cylindrical shape to form a tubing half.

Figure 4 is a perspective view of a half fin member.

Figure 5 is an end view of the assembled tubing prior to swaging the inside edges of the fins.

Figure 6 is a longitudinal section on the line 6-6 of Figure 5 showing the inside edges of the fins swaged against the interior wall of the tubing.

Figure 7 is an enlarged detail section on the line 7--7 of Fig. 5.

Referring to the drawings, the tubing of my invention comprises two similar semi-cylindrical halves 1, each as illustrated in Figure 3. Each half is formed from a fiat strip 2 of sheet metal such as illustrated in Figure 1. The strip is punched to provide a series of transverse slots 3 which are spaced apart at distances determined by the desired spacing of the fins. Said slots are of a width equal to the thickness of the fins which are ordinarily of the same gauge as the strip 2. For example, if the strip 2 is in thickness, the fins 4 will ordinarily be of the same thickness, and the slots 3 would be punched to a width of It will be understood, however, that the fins are not necessarily of the same gauge as the strip 2, as they may be either thinner or thicker than the strip 2.

Each of the semi-cylindrical halves 1 is provided with a pair of longitudinal flanges 5 along its side edges, and the length of the slots 3 is such as to extend to the corners where the cylindrical portions meet the flanges.

As hereinafter explained, the tubing halves and the half fins are assembled and then secured together in any suitable manner, as by spot welding, or riveting, or both, and in cases where riveting is intended the flanges 5 may also be punched to provide rivet apertures 7. Such apertures are also useful, however, in securing quick and accurate location in the jigs used in forming and assembling the tubing, and will usually be punched in the strips for this purpose even though it is intended to use welding in the assembly process.

The half fins 4, shown in Figure 4, are also made of sheet metal and are of an area designed to give the required heat transfer surface. Each half fin is provided with a semicircular notch 8 in one edge, the radius of curvature of the notch being slightly less than the radius of inside curvature of the tubing cylinder, so that, as shown in Fig. 5, when the fins are assembled with the tubing halves, the curved edges of the fins extend through the slots 3 to provide narrow margins which project beyond the wall of the tubing. After assembly, each projecting margin is formed into a head 9 which engages the interior wall of the tubing and not only effectively secures the fin to the tubing wall, but also seals the slots 3 against leakage. Such beads may be formed in any suitable manner, as by swaging or the like. In performing the beading operation, care must be taken to avoid expansion of the metal within the slots 3, as such expansion would tend to deform the tubing. Preferably, the heading tool is provided with a knurled surface which tends to cut the edges of the fins as they are worked, thus tending to facilitate lateral spreading of the metal. As a result the heads 9 will usually have a knurled or roughened surface.

The half fins 4 are provided with feet 10 at their edges adjacent the notch 8, which said feet project at right angles to the plane of the fins. Preferably said feet are punched to provide apertures 11 which, as in the case of apertures 7, may be used for convenience in assembly or for riveting, or both.

In assembling the tubing, it is usually convenient to first assemble each half tubing as shown in Figure 3 with a series of half fins as shown in Figure 4. Thus, with the half tubing held in a suitable jig, the half fins are set in place in the slots 3 and the feet 10 are spot welded or riveted to the flanges 5. Then two such half tubings are secured together, as shown in Fig. 5, either by spot welding or by rivets 12, as shown.

The swaging operation to form the beads 9 may be performed either before or after assembly of the two half tubings.

Alternatively, the tubing may be assembled by first assembling the two half tubings and securing them together along their abutting flanges. Then the half fins are set in place and secured to the tubing flanges. When this method of assembly is used, the swaging operation which forms the beads 9 will be performed after the assembly operations have been completed.

Finned tubing as above described may be formed of any desired metal including metals such as stainless steel, aluminum, magnesium and special alloys required in some situations for resistance to corrosion, many of which metals and alloys are either not suitable for use in the manufacture of finned tubing by conventional methods or are difiicult to use. Moreover, combinations of metals may be used if desired, so that the tubing halves may be made of one metal, while the half fins may be made ofa different metal. In.any-case, the thickness of the tubing wall may be considerably less than the thickness required in finned tubing of conventional construction.

One of the advantages of 'the invention is that it may beapplied-tothe manufacture oftubing of: a wide range of diameters. Whereas finned tubing of conventional constructionis.usuallyvlimitedrtodiameterstof 2" or less, it iseasily'possible .accordingto the presentinvention to produce tubing up to 6" in;diameter, andlargeirdiameters are possible, if desired.

Another. important advantage of the invention is the high.rate of heat transferwhichitmakes possible. This results in part from the .fact that the tubingwallcan be thinner than inconventional finned'tubing, and in part from the fact thatthe finsthemselves are in direct contact with thelgases within the tubing. Heat, therefore, may be conducted directly through thexfins without the interposition of ajoint between the tubing and exterior fins, which said joints" are frequently. faulty, and retard heat flow.

It will be understood that the invention may be variously modified and embodiedwithinthe scope of the subjoined claims.

I claim as my invention:

1. Pinned tubing for use in heat exchange apparatus comprising a pair of longitudinally extending semi-cylindrical members of relatively thin sheet metal, said members havinga series of opposed spaced transverse slots extending through the wall of said members, each of said members having longitudinal flanges extending along its side edges, said flanges being. secured together in abutting relationship to form a cylindrical tubing, and a seriesof half fins mounted on said members in abutting relation to said longitudinal flanges, said finshaving edges co-extensive with said slots extending through said slots into and engaging the interior Wall of the tubing.

2. Finned tubing as claimed in claim 1 in which the edges of said half fins which extend through said slots are provided with a bead engaging the interior wall of the tubing.

3. Finned tubing as claimed in claim 1 in Which each of said half fins is provided with feet projecting at right angles to the plane of the fin, and in which said feet are secured in abutting relation/to the flanges of said tubing.

4. Finned tubing as claimed in claim 1 in which each of said half fins is provided with feet projecting at right angles to the plane of the fin, in which said feet are secured to the flanges of said tubing, and in which the edges of said half finswhich extend through said slots are each provided with a semicircular notch having a radius of curvature slightly less than the radius of curvature of the tubing cylinder, and in which said notched edge is provided with a bead engaging the interior wall of the tubing.

5. Finned tubing as claimed in claim 1 in which said flanges are provided with a series of spaced apertures, each of said apertures being located midway between a pair of successive slots.

6. Pinned tubing .as claimed inclaiml inwhich said flanges are eachprovided with aseries of spaced-apertures, the aperturesrof opposed, abutting flanges being in registration, and inwhich each of said fins is provided with feet projecting at right angles. to the-plane of the fin, each of said feet having an aperture therein in registration withapertures in said' flanges and rivet-s passing through said registering apertures.

ReferencesCited in the file ofthis patent UNITED STATES PATENTS 406,332 Bayles July 2, 1889 933,371 Kane" Sept. 7, 1909 1,949,984 Walker Mar. 6, 1934 1,950,112 Jacocks Mar, 6, 1934 2,036,417 Laird Apr. 7, 1936 2,156,538 Maynes May 2, 1939 2,709,074 Gannon May 24, 1955 2,726,850 Buongirno Dec. 12, 1955 FOREIGN PATENTS 4,556 Great Britain of 1897 

